VISUAL CONDITION SURVEY OF PORCHE COCHERE THE HEIGHTS, MIDDLEBURY, VERMONT REPORT INTO EMERGENCY REPAIRS AND EXAMINATION OF FOOTINGS

Transcription

1 VISUAL CONDITION SURVEY OF PORCHE COCHERE THE HEIGHTS, MIDDLEBURY, VERMONT REPORT INTO EMERGENCY REPAIRS AND EXAMINATION OF FOOTINGS NIGEL COPSEY FOR TOM KEEFE OCTOBER 2003

2 The Heights is a significant 19 th Century mansion set in landscaped grounds on Route 30 south of Middlebury. It belongs to the Kaiser family. Its construction displays a high quality of craftsmanship and retains its original lime mortar, which is in a generally sound condition. All elevations have been painted with a brick-red wash which is beginning to degrade, particularly over the mortar joints. As far as the masonry is concerned, the main areas of concern are directly related to defective, or under-maintained rainwater goods. This has led to water running down the walls, exposing the soft bricks and mortar to frost attack. There have been occasional repairs to these areas with hard cement mortar, which has accelerated and exacerbated the degradation of softer masonry elements. The house is largely unoccupied. The immediate area for concern is the condition of the Porch Cochere, which was likely a later addition to the main house. An initial visit was made to The Heights during July The outcome of this visit was to propose a small programme of emergency repairs to the

3 north wall of this structure, in order to mitigate the potential for further damage during the winter of 2003 in lieu of a full analysis of the problem and more extensive stabilization/consolidation works in the near future. These proposed repairs were intended to be temporary and easily reversible, and were to include an inspection of the footings to the east pier of the porch, which appeared to be suffering significant subsidence. ANALYSIS The whole structure of the Porch Cochere is in some tension; the piers wanting to pull away and being held by a substantial timber collar beam, above which the masonry piers continue. Without the collar beam, the outward force of the heavy pitched roof would have caused greater deflection and sooner. It is difficult to fully understand the full implication of these stresses by visual inspection alone. Consolidation of the structure as is with minimum intervention would seem to be the priority. There is significant deflection to three of the four masonry piers, probably due to localized action of water causing subsidence within the stone footings. The level of the drive is some 5 inches lower than originally. This drop in the level of the drive has exposed the stone footing beneath the lowest course of brickwork, which has been covered with a red-tinted hard cement render. Behind this largely hollow render, the face of the stone footing is around 40mm behind the face of the brickwork, the first course of bricks (laid end-on, across the wall) cantilevering by this amount. The stone steps from the drive up onto the veranda have had a stone slab added to take up the drop in level.

4 The deficient grading of the drive has led the flow of rainwater and snowmelt to pass along the base of the east wall and to concentrate at the east end. The lower 2-3 feet of the north-east pier have subsided away from the masonry above en masse, by some 1 to 11/4 inches eastward. For this reason, an exploratory trench was dug to some 24 inches deep. Beneath a thin layer of turf and topsoil, the subsoil was of a soft sand, not sharp. The stone footing of the wall was built to a depth of some 8 below ground level, the stones being hand-dressed and laid in lime mortar. Below this there was stone, but of very much more thrown construction, apparently without being bedded in lime mortar (although this may have degraded and leeched away). The stones were at all angles and very rubbly. My analysis was that settlement within this lower layer, whether because of loose original construction, or because of water washing out fines, the one inch or so of settlement indicated by the subsidence of the masonry above could be readily accounted for. Furthermore, the pure sand subsoil would be unlikely to resist such movement. More water is added to the equation by the presence of rainwater down-pipes to the outside of the north wall at the west and east ends. These discharge at the base of the piers. A further factor

5 would seem to be the presence of a large tree some 5 yards to the southeast, the roots of which were present at the wall base when the hole was dug. In such light soil, trees would have to work hard to gain sufficient moisture from the ground, and the overall dryness of the ground will have increased as the tree has aged. This may well be a factor in the potential for subsidence of the masonry of the porche cochere. The sandy soil and form of construction of the footing, both of them free-draining would, however, reduce the likelihood of frost Heave as a major factor in any structural movement of the masonry. My conclusion was that at this stage the subsided masonry was unlikely to fall out over the coming winter, and that, although of concern, the construction of the footing was essentially sound for the moment. Some consolidation, jacking and pinning will be necessary in the near future. A rebuild of this section will probably not be necessary. Generally, there is significant deflection to three of the four masonry piers. The pier abutting the house (SW) shows up to one inch of movement. Only two tie-bricks bound it to the house. The uppermost of these has moved outwards beyond the wall-line of the original house. The rubble stone foundation is exposed. The movement in the brickwork is below the timber corbel, which is attached to the wall-plate/collar beam by a timber column, with brickwork above that appears stable. The masonry also twists towards the east by some three-quarters of an inch. There has been a loss of pointing mortar up to the normal level of winter snow.

6 There is similar deflection in the same directions to the NW pier. Also, sideways movement towards the west. This could be associated with the outward thrust of the inverted arch of the north wall. The arch is imposing significant thrust onto relatively slender piers. The wall-plate and the weight of the roof is, in turn, restraining the potential for outward movement resulting from the thrust of the arch. The soffit of the inverted arch receives considerable rain and snow precipitation, its pointing has failed in the past and it has been repointed with hard Portland cement-based mortar, which has failed in its turn, becoming loose. A lot of moisture, therefore, has tracked into the body of the wall, as well as running down its face. The failure of mortar joints to the wall face is consistent with this water run-off and with frost activity within the wall.

7 The subsidence at the base of the NE has been discussed above. There is around five-eighths of and inch of twist in the upper pier, below the corbel. There is very slight northward deflection of the SE pier beneath the timber corbel. TEMPORARY REPAIRS It was proposed that the arch soffit and brickwork below be repointed as necessary with a soft, sacrificial and readily reversible lime mortar, to arrest the ingress of moisture and to protect the masonry until such time as a more thorough-going repair could be carried out. The mortar mix was 1 part putty lime to 1 part hydraulic lime (NHL 3.5) to six parts sharp sand. The priority was to carry out an effective emergency and temporary repair. There was insufficient time to carry out colour-matching trials. My expectation was that after full-blown repair, the masonry would once again be lime-washed with a brick-red pigment, as originally. Much of the original pigmentation remains. On starting the work, it became necessary to remove and rebed some 5 bricks of the arch soffit, due to the complete degradation of the mortar within the hard cement pointing. The new mortar was pointed full and then beaten back with a stiff brush, being left on the full side to minimize the likely ingress of moisture. It was observed that the original lime mortar of the masonry was exceptionally hard for a lime mortar, perhaps too hard, and that this will have contributed to the spalling of the faces of some of the bricks and have reduced the overall vapour permeability of the mortar. This would account for the subsidence en masse of the lower section of the east pier. The mortar of the main house is softer and more appropriate to the relative softness of the bricks.

8 The success of a lime mortar depends upon considerable wetting of the substrate. This was done. Five days after the pointing, it was observed that the brickwork that had been wetted during preparation for and curing of the pointing has considerable salt efflorescence, such that the bricks were white. This is an indication of the amounts of ground-salts and, to some extent, sulphates introduced by the use of ordinary Portland cement mortars (and acid snow?) present in the wall. Whilst unsightly, better out than in. Salts are hygroscopic and draw moisture to themselves, and thus into the wall. The only course of action is to brush the salts off as they crystallize in drying conditions. Washing them off will send them back into solution and back into the wall. To a certain extent, the soft lime mortar will act as a sacrificial poultice, drawing salts into itself. This is a good thing in the long run.